1. Field of the Invention
This invention relates to the field of electrical transformers. More particularly, to a transformer designed to be used in conjunction with surface mounting technology for assembly onto a printed circuit board or the like.
2. Prior Art
Various designs, configurations and structures for electrical transformers are well-known in the prior art. A basic transformer is comprised of at least two closely coupled coils which form a primary and a secondary winding, respectively. The primary and secondary windings are physically disposed in such a way so that energy transfer is achieved by the movement of the electromagnetic flux lines, originating from the primary winding, move across the secondary winding, wherein energy transfer to the secondary winding is achieved. Although there are variations to this basic design, the general concept of energy transfer in a transformer is achieved by the movement of the electromagnetical flux lines across the secondary winding. In some instances, such as for a low frequency operation, the windings are wrapped about a ferrite core. In most instances, the windings are typically formed from copper or plated copper wire.
In manufacturing a typical prior art transformer, the wires are machine or hand wrapped to form the various windings. The windings are wrapped about a ferrite or an air core. Then the whole unit is molded or laminated and sometimes encased in a metal housing with the terminals of the windings being located outside of the casing. Power transformers, which are used in a power supply, are typically designed to be mounted by fasteners, such as screws and bolts, because of their size and weight. Once these prior art transformers are physically mounted onto a circuit board or chassis, then hand soldering of electrical connections to the various terminals of the transformer are required. The manual soldering operation is not only time consuming but costly due to the use of manual labor. Even with the use of automated machinery, the prior art transformers still require a special soldering step, typically performed as a manual operation, for connecting the electrical wires to the various transformer terminals.
One segment of the automated printed circuit (PC) board assembly entails the practice of surface mount technology (SMT). In a typical SMT operation, an unassembled PC board enters the assembly station of a production line during a manufacturing process. The PC board is positioned proximal to an automated assembly tool, such as an automated robotic mechanism. In a typical automated assembly process, a tray of components, which components are to be assembled onto the PC board, are also disposed near by. The automated equipment selects a given component and positions the component to the appropriate location on the PC board. With SMT, the leads of the component are disposed through appropriate openings on the PC board, or in other instances placed onto the surface of the PC board without penetrating through the PC board, and are physically affixed and electrically coupled to the PC board, such as by soldering or welding. A robot mechanism uses a variety of sensing devices, including weight sensors and optical scanners to identify and align the various components for placement onto the PC board. These techniques of surface mounting various components onto a PC board by the use of automated equipment is well-known in the prior art.
However, the robotic mechanisms are designed to operate with relatively small size and light weight components, such as resistors, capacitors, and semiconductor chips. Larger and heavier components, such as conventional transformers cannot be readily adapted for SMT. Of course larger robotics mechanisms can be used, however, because of the prohibitive cost of larger robotics arms, for example, it is typically economically unsound to utilize significantly larger robotics mechanism just to be able to automatically mount transformers onto the PC board. In some instances, where the robotics mechanism is capable of lifting and placing a transformer onto the PC board, the terminals of the transformer do not lend themselves to the surface of the PC board for surface mounting. As a result, conventional transformers suffer from the disadvantage of needing the less efficient manual placement onto the PC board and the subsequent manual soldering of the electrical connections. Without the use of highly specialized robotics mechanisms, especially adapted for mounting such transformers, prior art transformers cannot be readily used for surface mounting onto a PC board.
Additionally, the current prior art transformer designs, especially the power transformers, are less efficient. Also, heat dissipation is a concern on a closely populated PC board. One method to increase heat dissipation is to increase the exposure of a greater area of the tranformer core. However, a configuration that advantageously leaves the windings exposed, increases the likelihood of stray inductance. On the other hand, surrounding both the transformer windings and the core increases the weight and the size thereby increasing space displacement on the PC board. Moreover, beyond the problems of weight, size, heat dissipation, and structure for use with SMT, the windings may not be precise as to their placement and separation. That is, because the windings are comprised of coils wound on top of each other, the placement and separation of the windings is difficult to precisely achieve with typical prior art transformer manufacturing methods.
It is appreciated that what is needed is a heat efficient, relatively small size, light weight and cost effective transformer that can be used with surface mount technology. The present invention describes a surface mount transformer which can be used with automated assembly equipment and which is cost effective.